1. Field of the Invention
The present invention relates to a call restricting method in a packet switching network and a network controller having a call restricting function and, more particularly, to a call restricting method which, when it is anticipated that packet communication with a transmission quality demanded by respective terminals becomes difficult due to the fact that an excessive quantity of data causes the network to fall into its congestion state, restricts the calling operation of call sending terminals to thereby previously prevent the network from being shifted to the congestion state, and a controller embodying the method.
2. Description of the Prior Art
Referring to FIG. 1, there is shown an example of a packet switching network, which includes packet switching nodes 12 directly or indirectly connected to various sorts of medium terminals 11 such as data terminals, voice terminals, picture terminals and so on, for generally controlling the respective terminals and for converting communication data geneated at these terminals into data having a packet format to be transferred and also converting packet format input data received through the packet switching network from destination terminals, into data having such a format that the data received terminal can reproduce, network controllers 13 disposed within the respective packet switching nodes 12 for controlling mainly network control between the packet switching network and the respective packet switching nodes on the basis of a calling data sent from the terminals 11, subscriber lines 14 connected between the terminals 11 and the respective packet switching nodes 12, trunk lines 15 connected between the packet switching nodes 12, terminal interfaces 17 connected between the terminals 11 and the packet switching nodes 12 for providing a calling-data informing function when the terminal 11 is not provided with the calling-data informing function to the assocaited network controller 13, packets 16 being transferred on the trunk lines 15 being shown in a model form.
Assume now that it becomes necessary to transfer a communication data from one terminal to another. Then the terminals 11 and the packet switching nodes 12 execute the sending or transfer operation of necessary data in such a manner as to be explained.
(1) A call demander terminal first sends a calling data including the address of a destination terminal and the address of its own terminal to the associated packet switching node connected to its own terminal (more accurately, to the network controller 13 provided in the associated packet switching node). For a terminal not provided with the calling-data informing function to the associated network controller 13, the terminal sends the calling data through the terminal interface 17 to the associated network controller 13.
(2) The packet switching node (the network controller 13) having received the calling data in this manner, selects, on the basis of the calling data, a route by which the communication data of the terminal in question is to be transferred and transfers the calling data in a packet format to the packet switching node which is in the selected route and which is adjacent to its own node.
(3) The adjacent packet switching node (network controller 13) having received the calling data and the subsequent packet switching nodes, similarly select the next route and eventually transfer the calling data in the packet format to the packet switching node to which the destination terminal is connected.
(4) The packet switching node having the destination terminal connected thereto, calls the destination terminal, confirms that the destination terminal is in its answerable state and then returns a call setting completion data of the packet format through the same route back to the caller packet switching node.
(5) The caller packet switching node, when having received the call setting completion data, informs the caller terminal of the call-setting completion data.
Through the above series of processings, the calling operation has been completed. Under this condition, the route secured in the aforementioned manner is maintained until any one of the terminals logically connected to each other issues a disconnection request. On the maintained route, transaction of the communication data between the terminals is carried out in the form of the packet 16.
With such a packet switching network that transmits communication data in the packet form, packets themselves are asynchronously transmitted and reach the respective target terminals through various routes. For this reason, it sometimes occurs that packets are convergedly sent to the particular packet switching node or to the particular trunk line, that is, a so-called traffic congestion takes place.
For the purpose of avoiding such a traffic congestion, a buffer having a suitable capacity is usually provided within each of the packet switching nodes so that the associated terminal is connected through the buffer to the associated trunk line.
The use of the buffer, however, has also involved a new disadvantage of "packet transmission delay". The packet transmission delay results from the fact that the packet must be transmitted through the buffers to the target terminal. Such transmission delay is not so important when the packet switching node is connected with a terminal requiring a relatively low transfer rate of communication data such as a data terminal, but cannot be made negigible when the packet switching node is connected with such a terminal having strong real time data as a voice terminal or with such a terminal having a wide range of data largely changing in quantity as a picture terminal.
Under such circumstances, there has been recently suggested a technique of restricting the calling operation from terminals to avoid the traffic congestion and put to practical use.
Shown in FIG. 2 is an internal configuration of the network controller of the packet switching node based on such a calling restricting system and convetionally employed in a packet switching network. As shown in FIG. 2, the network controller 13 comprises a calling protocol analyzer 1, a network administrator 2 and a route decider 3. The terminal 11 is connected to the calling protocol analyzer 1.
In the network controller 13, the address data of the destination terminal contained in a calling data issued from the terminal 11 is analyzed at the calling protocol analyzer 1 which in turn informs the route decicer 3 of the analized address contents.
The route decider 3 decides a route, i.e., the trunk line or lines of the route leading to the designated destination terminal on the basis of the informed address data contents and transfers a call through the calling protocol analizer 1 to a packet switching node provided in the decided route and adjacent to its own packet switching node. At this time, when the network administrator 2 already informs the route decider 3 of a data indicative of occurrence of a trouble in the trunk lines of the decided route or a data indicative of occurrence of a congestion on the trunk lines, the route decider 3 refuses reception of a call from the terminal 11.
With such a packet switching network, when a trouble or a congestion takes place on one of the trunk lines, the network controller 13 automatically restricts the call using the trouble or congestion trunk line. For example, when a congestion occurs on the trunk line, the congestion is prevented by means of the network controller 13 from becoming more excessive. In other words, even when a congestion takes place, it can be removed with relative ease.
This calling restricting method, however, can restrict the calling operation through the above network controller 13 only when a trouble occurs on the trunk lines of the every time decided route or only when a congestion actually takes place. In other words, if a congestion does not actually take place, then the the network controller 13 will unconditionally accept the call even under such a condition that the trunk line is about to be put into its congestion state. Under such an immediately-before-congestion state, when the network controller 13 accepts a call from a voice or picture terminal having a large quantity of communication data output, the trunk line is put into the congestion state with a high possibility and thus it becomes difficult to ensure a stable packet transaction with a transmission quality demanded by the terminal.